CSE 420Intermediate Code Generation

Lecture 13

Conversions between primitive Conversions between primitive types in Javatypes in Java

Introducing type conversions into Introducing type conversions into expression evaluationexpression evaluation

Abstract syntax tree for the Abstract syntax tree for the function definitionfunction definitionfun length(x) = if null(x) then 0 else length(tl(x)+1)

This is a polymorphic function in ML language

Control FlowControl Flow

Boolean expressions are often used to:

•Alter the flow of control.•Compute logical values.

Short-Circuit Code

Flow-of-Control Flow-of-Control StatementsStatements

Syntax-directed definitionSyntax-directed definition

Generating three-address code for Generating three-address code for booleansbooleans

translation of a simple if-translation of a simple if-statementstatement

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BackpatchingBackpatching• Previous codes for Boolean expressions insert

symbolic labels for jumps• It therefore needs a separate pass to set them to

appropriate addresses• We can use a technique named backpatching to avoid

this• We assume we save instructions into an array and

labels will be indices in the array• For non-terminal B we use two attributes B.truelist

and B.falselist together with following functions:▫ makelist(i): create a new list containing only I, an index into

the array of instructions▫ Merge(p1,p2): concatenates the lists pointed by p1 and p2 and

returns a pointer to the concatenated list▫ Backpatch(p,i): inserts i as the target label for each of the

instruction on the list pointed to by p

Backpatching for Boolean Backpatching for Boolean ExpressionsExpressions

• •

Backpatching for Boolean Backpatching for Boolean ExpressionsExpressions•Annotated parse tree for x < 100 || x > 200 &&

x ! = y

Flow-of-Control Flow-of-Control StatementsStatements

Translation of a switch-Translation of a switch-statementstatement

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